Fluid pulse surge control indicator



April 26, 1966 L, T P ET AL 3,248,043

FLUID PULSE SURGE CONTROL INDICATOR Filed June 25, 1963 7 Sheets-Sheet 1can/rem J T JET-ON J57- mLl E OUTPUT FLOW CONT/20L JET M \S'UPPLY JET vV012 TEX WIL VE 4,454 a. TAPL/N 77/0/1595 1 7" 6 04/1 0 1 650265 77 B(/2 7'0 CM! 7' 01V fl. ill/BEN INVENTORS A 7'TOE/VE Y April 26, 1966 B.TAPLIN ET AL 3,248,043

FLUID PULSE SURGE CONTROL INDICATOR Filed June 25, 1963 7 Sheets-Sheet 524 2/0 g y/s2 22f??? GATED SPA-E0 com/mm T L051. 5. Tar-Luv THO/$076 E.THOMPSON 050265 7: Buera/v 01.4fm A. HUBE'N 1N VENTORJ MZZWW ,9 TTOENE YApril 26, 1966 TAPUN ETAL 3,248,043

- FLUID PULSE SURGE CONTROL INDICATOR Filed June 25, 1963 7 Sheets-Sheet7 MEL B. TfiFL/N THO/1:96 E THOMPJOA/ GEORGE 7. BURTON CLHYTO/V fl-I'll/BEN INVENTORF radiation levels.

United States Patent FLUID PULSE SURGE CONTROL INDICATOR LaelB. Taplin,Thomas E. Thompson, George T. Burton,

and Clayton A. Huben, Southfield, Mich., assignors to The BendixCorporation, Southfield, Mich., a corporation of Delaware Filed June 25,1963, Ser. No. 290,528 4 Claims. (Cl. 230-415) gine control system andis particularly advantageous for 7 present day high speed aircraft ornuclear applications requiring high reliability in extreme temperatureenvironments or control systems requiring tolerance for highAdditionally, in such applications Weight considerations are of utmostimportance whereas said fluid pressure interaction valves are adaptableto be packaged in small structures and as they have no or few movingparts the wear factor is eliminated thus permitting greater freedom inselecting materials on a weight or environment basis.

Accordingly it is an object of the present invention to provide acontrol utilizing pure fluid amplifiers of the sti'eam interaction type.

It is another object of the present invention to adapt said pure fluidstream interaction amplifiers and principles as useful parameter sensorssuch as speed, surge and the like.

It is a still further object of the present invention to provide basiccomputing components operating on a time-dpulse or digital principle toeflectively utilize said stream interaction amplifiers to computecontrol requirements based on sensed and input reference requirements.

Other objects and advantages of the present invention will becomeapparent on consideration of the descriptio and appended drawingswherein:

FIGURES 1 and 2 are schematic representations of prior art pure fiuidamplifiers of the stream interaction p FIGURE 3 is a functional blockdiagram of a basic engine speed control loop;

FIGURE 4 is a functional block diagram of an engine control systemincluding the speed control loop of FIG- URE 3 with additional surgelimiting functions;

FIGURE 5 is a schematic drawing of a pneumatic tachometer or speedsensor;

FIGURE 6 is, a schematic drawing of a pneumatic tuning fork oscillatoror fixed frequency pulse generator;

FIGURE 7 is a schematic drawing of a pneumatic tuning fork oscillatorwith mechanically variable frequency pulse output;

FIGURE 8 is a schematic drawing of an error signal computer and digitalto analog signal conversion devices;

FIGURE 9 is a schematic drawing of a fuel control subsystem forcontrolling engine fuel delivery in response to a pneumatic signal;

FIGURE 10 illustrates air flow pattern over an engine compressor bladeand impending stall detection;

FIGURE 11 is a functional block diagram of surge subsystem;

FIGURE 12 is a schematic drawing of a gate valve for selectivelyblocking a pulse signal in response to a single blocking input;

FIGURE 13 is a schematic drawing of a gate valve for selectivelyblocking a pulse signal in response to two (or more than one) blockingsignal;

FIGURE 14 is a schematic drawing of a pulse shaper device; and

FIGURE 15 is a drawing of an engine fuel system incorporating theteachings of the present invention.

Two prior art examples of pure fluid amplifiers of the streaminteraction type are illustrated schematically in FIGURES 1 and 2.

The jet-on-jet amplifier or valve is shown in FIGURE 1. This conceptinvolves the power jet 2 supplying high pressure fluid which, whenunrestrained, strikes the two receiver passages 4 and 6 symmetrically;thus building up equal pressures in each receiver line. If a controljet,

such as illustrated by jets 8 or 10, is imposed on the power.

jet laterally, the combined momentum of the two jets causes a vectorchange which allows impingement of the combined jet on one hole to besomewhat larger than the other receiver hole depending on the initialmomentum of the control jet. The pressure level of the control jet isconsiderably below that of the power jet and this jet-onjet amplifierhas been demonstrated to have power gains ranging from 10:1 to :1.Differential pressure gains, that is the diiferential pressure betweenreceiver passages 4 and 6 ratio to the differential pressures between apair of control jets Sand 10 can be as high as 50:1.

Another type of all fluid valve or amplifier is the vortex valve asshown in FIGURE 2. Here a supply jet 12 is brought into a cylindricalcavity defined by the wall 14 radially. A control jet 16 is located atright angles to the supply jet and tangential to the wall 14. Thecontrol jet need not necessarily be introduced in the same vicinity asthe supply jet, but may be tangentially located around. The exit flow istaken out the wall 14 in many places. through a hole 17 located in thecenter of the device. If the control jet alone is turned on, it is seenthat a vortex sheet will be established Within the cylindrical chamber.Introducing the supply jet alone will cause a radial flow across thecavity to the exit hole 16. With the supply jet flow established, if thecontrol jet fiow is increased, a vortex build-up occurs causing acentrifugal pressure to exist at the supply jet port so that increasingthe control jet fiow causes the actual supply flow to be decreased. Thepower gain for this device'has been established at around 10: 1 forgases and approximately 20:1 for liquids. That is, the flow workrequired at the control jet to apreciably cut down the flow work at thesupply jet is approximately 10% of the initial flow work entering thesupply jet. The incremental gain associated with the device, that is,the change in supply flow for a small change in control jet flow hasbeen reported as high as 100,000: 1. A considerable amount of Work isgoing on in basic valves of the types described above and similarvarieties which are generically referred to herein as stream interactionfluid amplifiers. The species shown in FIGURE 1 is referred to herein asjet-on-jet amplifier whereas the FIGURE 2 species is referred to as avortex amplifier.

Engine control parameters The present invention as disclosed herein isapplied to a gas turbine engine, particularly to fuel delivery thereto,

however, as will be apparent some of the basic computing and sensingsubcomponents will have a broader application and for these subsystemsthe present description should be considered as illustrative and notrestrictive.

The primary quantity involved in the control of a gas turbine engine isengine speed or speed of the turbine and/ or compressor assembly. Thedesired level of engine speed is selected by the pilot and is introducedinto the engine control system via a throttle normally located in thecockpit.

Referring to FIGURE 3, there is shown a functional block diagram of abasic engine speed control loop wherein a pilot control throttle isrepresented by the block 18. Throttle position is transmitted viamechanical linkage represented by block 20 to an input transducer 22which is a control device for converting the throttle position signal toa pneumatic pulse signal. The pneumatic signal from transducer 22 isapplied to the error computer section 24 for comparison with speed pulsefeedback signal supplied by connection 26 to produce an error signal.Error computer 24 additionally converts the digital pulse logic to acontinuous analog signal suitable for positioning physical apparatus andthus is also designated as a digital/analog converter. The output ofcomputer 24 is supplied to the fuel control subsystem 28 (fuel valve) tocontrol the rate of fuel delivery to the engine 30 and thus affectengine speed. Actual engine speed output is supplied by a mechanicalrotation through connection 32 to speed sensor 34 where it is convertedto a pneumatic pulse signal to comprise the feedback quantity 26 andwhich is adaptable for comparison with the output of transducer 22. Thissystem comprises a basic speed con trol loop which provides accuratecontrol of engine speed and is functionally adapted to utilize the pulseinformation to control the fuel control subsystem. In operation, thepilot requests his speed by positioning throttle 18. If the requestedspeed differs from the actual speed supplied by feedback connection 26an error signal is generated in computer 24 which is supplied to thefuel subsystem 28 for changing fuel flow andthus speed in a direction tocorrespond with that requested.

Whereas speed is the primary controlled quantity of interest in a gasturbine engine control, practical behavior of jet engines requiresconsideration of engine compressor surging. Surging results in reducedcompressor etficiency and in potential vibration damage to thecompressor structure and must be avoided. Surging is influenced by fuelflow and can be avoided by appropriate limitations placed on fueldelivery in response to sensed surge conditions.

FIGURE 4 shows a functional block diagram of an engine control systemincluding the basic speed control loop of FIGURE 3, whereincorresponding blocks bear the same numerals and the engine 30 is brokendown into its main subcomponents of a compressor section 36, acombustion chamber 38, and a turbine 40. -A surge control system isadded in FIGURE 4. A surge sensor represented by block 42 is providedand connected to the compressor 36 by connection 44 for sensing animpending surge condition. If surge is imminent, surge sensor 42 whichis connected at 46 to the computer section 24 is operative to overridethe speed control and avoid surge by reducing the error signal withincomputer 24 and thus reducing fuel. Surge prevention functionally servesto override the speed control loop during periods when dangerous surgeconditions exist. Considering the auxilliary nature of the surge system,the speed and surge control systems can be discussed separately. Sincethe speed control system is primary, it is discussed first.

Speed control loop The basic speed control loop functionally shown inFIGURE 3, consists of four basic subcomponents shown in FIGURES through9. Considering that one prime object of this invention is to utilizestream interaction type fluid amplifiers, a digital approach employingfrequency-modulated fluid pulse trains is employed for the followingmajor reasons:

(1) Analog signals are categorically less suitable for signaltransmission where non-linearities, distortion, and noise levels aresignificant.

(2) Though generally having appreciable non-linearity, most known stream.interaction amplifiers have fast switching response time whichmake themideal for digital applications when linearity is of decreasedimportance. In this application where speed, and surge are the primarysensed conditions, dig-ital sensors of extreme accuracy have beenachieved with very simple and reliable designs.

(3) In general, with a digital approach, reference speed and surgesignals can be generated as frequency signals which are stronglyresistant to distortion or masking by noise.

Referring to FIGURE 5, there is shown a pneumatic tachometer or speedsensor which functions to convert a mechanical rotational velocity intoa pneumatic pulse signal wherein the pulse frequency varies with speedto accomplish the function indicated by block 34 of FIG- URE 3.

The pneumatic tachometer comprises a supply chamber 58 containing a highpressure source, P a connecting transmission line 60 terminating with ajet nozzle 62 and containing a restrictive orifice or bleed member 64upstream and in series with nozzle 62 to define a chamber Ctherebetween. An output line 66 having a bleed 67 is connected to lines60 at chamber C. A rotatable gear 68 has a series of spaced teeth orflapper valves 70 which rotate in a close proximity to nozzle 62. Inthis device,

the gear 68 is connected by shaft 72 to the engine to ro-- tate inproportion to turbine speed. As a tooth 70 goes by nozzle 62 andrestricts the flow, a positive pressure pulse is developed within thechamber C and is transmitted through restriction 67 as an output throughline 66. The

pulse frequency is f=n w (pulses/ sec.) where n is the number of teethand w is the rotation speed of gear 68 in revolutions per second. Thispneumatic tachometer As functionally shown in FIGURE 3, blocks 18, 20and 22 collectively produce a pneumatic pulse output repre-' senting adesired engine speed value selected by the pilot or operator. This isaccomplished in the present invention by providing a fixed reference orknown frequency pulse oscillator or generator with an operatoradjustable means for varying the reference frequency with speed demand.

Referring to FIGURE 6, there is shown a pneumatic tuning fork oscillatoror pulse generator for producing a known and fixed frequency pneumaticpulse train. The tuning fork oscillator comprises a tuning fork 76 asthe frequency determining element having a pair of tines 78, one ofwhich is arranged in close proximity to a nozzle 80. As with the speedsensor, a high pressure, P contained in supply chamber 82 is connectedby transmission line 84, having bleed 86, to nozzle and an output line88 is connected to line 84 intermediate to bleed 86 and nozzle 80. Tine78 vibrates at its natural frequency alternately opening and closingnozzle 80 causing pressure pulses in output line 88 at its naturalfrequency or a known reference value. This oscillator is self-excitingwhen air pressure is supplied by nozzle 80 and requires no additionalinitiation or excitation means.

In FIGURE 7 there is shown a similar pneumatic tuning fork oscillator orpulse generator except that means have been provided to vary thereference frequency value in response to a mechanical position as may beapplied by a throttle. The basic tuning fork oscillator may be the sameas that shown in FIGURE 6 and bears the identical,

. numerals with the addition of a movable wedge or tuning slug 90clamped between tin-es 78 and having a position ing rod or connection 92for adjusting the tuning slug longitudinally of the vibrating tines andvarying the effective length thereof. Movement of slug 92 to vary theeffective length of tines 78 alters the vibrating frequency.

For example, commercially available tuning forks so adapted have beenfound to produce satisfactory frequency variations of the order of 3:1-which is an acceptable range of variation for a pilots command signal.

The error computer and converter represented by block 24 of FIGURE 3performs two basic functions which are as follows: p

(1) Comparing actual speed pulse signals produced by sensor 34 withrequested speed pulse signals from throttle 18, linkage 20 andtransducer 22 to develop a speed error signal proportional to thedifference between actual and requested speed.

(2) Converts digital pulses to a continuous analog signal adaptable topositioning a fuel valve or other physically movable output member. a

The error computer and converter is shown in greater detail in FIGURE 8.This circuit consists of a high pressure supply chaml'oer 90, Psupplying pneumatic pressure to main supply jet 92. Immediatelydownstream of supply jet 92 is a deflection chamber 94 which in turn isconnected to receiving chamber 96. Near the opposite or right side wallof receiver chamber 96, as viewed in FIGURE '8, are arranged ventpassages 98 and 100 connected to a low pressure region such as theatmosphere so that the general pressure level in receiving chamber 96 islow. A primary vent passage 102 has an opening 104 in the right sidewall of chamber 96 in alignment with supply nozzle 92 so as to normallyreceive the high pressure stream being ejected by the supply nozzle. Themain supply stream passes through primary vent passage 102 throughbellows chamher 106 and out vent passage 108 to the atmosphere. Spacedsymmetrically on opposite sides of vent opening 104 are a pair of outputopenings 110 and 112 which are connected to output passages 1 14 and 116respectively. Output passage 114 communicates with the interior of afirst bellows or pressure responsive member 118 contained in bellowschamber 106 and secured to its upper end wall. Output passage 116 issimilarly connected to a second bellows 120 secured to the lower endwall of chamber 106 and aligned with bellows 1 18. The free ends ofbellows 118 and 120 are connected by a rod 122 so that rod position is afunction of the difference in pressures acting on the opposed bellows.An angularly' movable output linkage 124 is pinned to rod 122 at 125 formovement therewith. Output passages 1'14 and 116 are additionallyconnected to feedback passages 126 and 128 respectively, each containinga b-leed 130 and 132 and terminating at nozzles 134 and 136 exhaustinginto deflection chamber 94 on opposed sides thereof and generallytransverse to the main supply stream flow from nozzle 92.

Two control passages 138 and 140 terminate with control jets 142 and 144respectively into deflection cham ber 94 generally transverse to thestream flow from main supply jet 92 on opposed sides thereof.

With no control signal supplied by either control passage 138 or 140, acontinuous stream of high pressure air will be ejected by supply nozzle92 traversing deflection chamber94 and receiver chamber 96 where it willimpinge on primary vent opening 104 and be transmitted through passage102, chamber 106 and vent 108 to the atmosphere. This flow will have nopositioning effect on rod 122. To the extent it causes a pressureincrease in bellows chamber 106 this pressure acts equally. on opposedbellows 118 and 120 and is balanced out. To the extent scatteredportions of the main supply stream do not enter primary vent opening104, they will be either exhausted through vents 98 and orimpingesubstantially uniformly on symmetrically spaced outlet ports and112 causing equal and offsetting pressure increases in [bellows 118 and120.

If a pressure pulse train control signal is supplied to control passage138, designated input A, it will be directed by control jet 142transversely against the main supply stream and deflect the main streamdownwardly in the direction of outlet signal port 112 to produce anamplified pulse output in line 116 and bellows 120. At the conclusion ofeach control input pulse in passage 138, the main supply stream willsnap back to its original alignment with primary vent 104. Consequently,the pulse period of the output signal A corresponds with the pulseperiod of input signal A. A second control pulse, inputB, is applied tocontrol passage 140 where it is similarly operative to deflect the mainstream into outlet passage 1 14. When the pulse frequency of inputs Aand B are equal, the main supply stream will be deflected an equalnumber of times per time unit towards outlet passages 114 and 116causing an equal and offsetting build-up in pressure within bellows 118and 120. If, however, there is a disparity in pulse frequency betweeninputs A and B a pressure unbalance H in the bellows is created toposition rod 122 and linkage 124. For example, should the pulserepetition frequency of input A be 400 c.p.s., while that of input B is350 c.p.s., for each second, bellows will receive an average of fiftyadditional pulses over bellows 118. Bellows 118 and 120 have arelatively large volume and act as accumulators or integrators whereinthe pressure level in each is a function of the pulse frequencyreceived. Thus in the assumed example, the pressure level in bellows 120will be greater than that in bellows 118 thus positioning rod 122upwardly and angularly positioning output linkage 124 clockwise. If thepulse frequency of input B were greater than input A, the pressure inbellows 118 would be the greatest, positioning rod 122 downwardly. Sincebellows have their own inherent resistance to deformation the degree rod122 is positioned, is dependent on the magnitude of pressure differencewithin the bellows which in turn is dependent on the difference in pulsefrequency between inputs. Of course, were the bellows deformationresistance is insuflicient or diaphragms are used, springs maybe used toestablish proportionality.

Thus the pressure difference between bellows 118 and 120 to move rod 122is proportional to the difference in frequencies or error between inputsA and B. Moreover the device has converted the digital pulse typeinformation to a continuous analog type signal positioning linkage 124.

Feedback means '126 and 128 have been provided in order that a degree ofgain control may be obtained. For example, as a pulse input A is appliedit diverts the main supply stream to passage 116 whereby a certainportion of the output pulse, depending on the size of bleed 132, will bedirected through feedback flow path 128 out nozzle 136 into deflectionchamber 94 in opposition to the input flow from nozzle 142. The feedbackflow thus subtracts or opposes the control flow and by varying the sizeof bleed 132, by replacement, the relative quantities may be establishedto provide a desired gain. The feedback flow in passage 126 operates ina similar manner in opposition to input B.

When feedback passages 126 and 128 have appreciable volume (which may beintentionally added) pressurization of passages 126 and 128 can bedelayed with consequent delay in pressurization of nozzles 134 and .136respectively. In this feedback configuration, this delayedpressurization results in a frequency variant gain control whichprovides an output differential pressure across bellows 118 and 120which is not only proportional to differential input (A-B) but alsoproportional to the time rate of change of the differential input (A-B).

In FIGURE 9 there is shown a fuel controlling sulbsystem 28 forutilizing the angular displacement of linkage 124 of the error computeras an input signal and metering a rate of fuel delivery in response tothis input.

Fuel from a source, not shown, is supplied to a main fuel passage 150.Low pressure supply fuel'is designated P In the upstream portion of mainfuel passage 150 there is disposed at high pressure gear pump 152 forpressurizing fuel to a relatively high value designated P Fuel from pump152 flows rightwardly through passage 150 through orifice or valve seat154 where it is metered and continues out passage 159 as metered fuelwhere it is adapted to be supplied to the manifold or fuel deliverynozzles of an engine. Metering orifice or valve seat 154 produces apressure drop or loss so that metered fuel is at a lesser value than Pand is designated P The pressure drop or head P -P is the metering head.

Metering head P P is maintained at a constant value by a by-pass valvegenerally indicated at 156. By-pass valve 156 includes a double portedpressure balanced valve 156 controlling P pressure fuel through valveseats 160 and 162 to bypass conduit 164 which returns fuel to the inletor low pressure side of pump 152. Valve 156 is controlled by diaphragm166 peripherally secured to the control housing and secured at itscenter to rod 168- on which the double valve portions are mounted. Ppressure fuel is supplied to the lower side of diaphragm 166 by conduit170 Whereas P pressure fuel is supplied to the upper side by conduit 172so that metering head P -P acts on diaphragm 166. An adjustaible headspring 174 provides a relatively constant downwardly or valve closingforce on diaphragm 166.

The force balance on diaphragm 166 established by spring 174 acting in avalve closing direction and the metering head P P acting in a valveopening direction maintains the head across valve seat 154 at asubstantially constant value. Should P P tend to increase, the by-passvalve is moved in an opening direction, by passing more fuel throughconduit 164. This decreases the fuel flow in conduit 150 downstream ofthe by-pass valve reducing P P to its selected value. Should P Pdecrease, the reverse action occurs whereby more fuel flows throughconduit 150 and valve seat 154 raising P P in a corrective direction.

Metering valve 176 is operative with the valve seat 154 to control theeffective area of fuel metering orifice. A hydraulic servo piston 178 issecured to the end of the metering valve and is slidable in a bore inthe control housing to define a first control fluid chamber 180 and asecond control fluid chamber 182 on opposed piston sides. P pressurefluid from main conduit 150 is transmitted via passage 184, servo valvechamber 186,

rate bleed 188 in branch passage 190, and passage 192 I to first controlfluid chamber 180 where it acts on one side of piston 178 having thesmaller effective area, tending to move valve 176 in a direction toincrease effective area and thus rate of fuel delivery. Pressure inchamber 180 is designated P to distinguish from P fluid upstream of ratebleed 188. A controllable pressure servo fluid (P is supplied to secondcontrol fluid chamber 182, from P fluid source in servo valve chamber186, through servo orifice 194 and passage 196. Chamber 182 is alsoconnected to a low pressure reservoir P through passage 198 having servobleed 200. P fuel in chamber 182 acts upwardly on piston 178 over thelarger surface of piston 178 and in opposition to P fluid in chamber180. P pressure is controlled by establishing a controlled pressure dropthrough servo orifice 194 by means of the pivot input lever 202 which issecured to the output linkage 124 of the error computer mechanism ofFIGURE 8, a portion of which is re-illustrated in FIGURE 9. The end ofinput lever 202 is arranged in close proximity to servo orifice 194whereby the P P pressure drop is controlled by angular movement of lever8 202 whichthus acts as a servo control valve. A rate feedback force issupplied to lever 202 by means of bellows 204 in chamber 186 which hasits movable end pinned at 206 to lever 202. Bellows 204 is fixed at itsother end to the control housing and communicates through passage 208with passage 192 downstream of rate bleed 188.

The servo system for positioning metering valve 176 may be termed anintegrating system inasmuch as piston.

178 will move a distance proportional to the integral with respect totime of the deviation of input lever 202 from its neutral or nullposition. Operation of the fuel subsystem is as follows:

At a stable or no-movement condition of piston 178 the fluid pressureforces acting on piston 178 are in balance with P having a pressurevalue a certain fixed percentage less than P corresponding closely withthe area ratio on opposed piston sides. Expressed mathematically, andneglecting fluid pressure end loading on valve 176:

where A 180 equals the area of piston 178 communicating with P pressurein chamber 180 and A 182 is piston area exposed to P fluid in chamber182.

Re-expressing the above equation:

where K is a constant of less than one representing the area ratio.

There is one position of input lever 202 termed its null position whichwill establish the balancing P /P pressure ratio by controlling the P Ppressure drop through serve orifice 194. If lever 202 deviates from thisnull position as for example in a direction closer to servo orifice 194,the P P pressure drop is increased thus lowering the value of fpressure. This causes a force unbalance across piston 178 causing it tomove downi wardly. Deviation away from null position by lever 202 causesP to increase moving piston 178 upwardly.

The rate at which piston 178 moves is controlled by is also applied tobellows 204 to produce a feedback force on input lever 202 opposing itsmovement from null, proportional to piston velocity.

By means of the rate feedback force applied to input lever 202 inopposition to its movement, the degree of deviation of lever 202 fromits null position is caused to be proportional to piston velocity. Thisis a characteristic of an integrating servo mechanism since if the rateof movement or velocity of piston 178 is proportional to lever deviationthen the total piston displacement becomes the integral of leverdeviation taken with respect to time since velocity is a time relatedquantity.

To summarize briefly the operation of the speedloop and combining thedevices of FIGURES 5, 7, 8 and 9, a variable pulse frequency referenceindicating desired engine speed is generated by the pneumatic tuningfork oscillator of FIGURE 7. The pulse output line 88 may be connectedto input line 138 of the error computer of FIGURE 8 to comprise input A.The pulse frequency output from line 66 of the pneumatic tachometer ofFIGURE 5 may be connected to line of the error computer to compriseinput B. The error computer positions linkage 124 proportionately to thepulse frequency error between the desired speed reference of input A andactual speed reference of input B. Linkage 124 is directly connected tothe input lever 202 of the fuel subsystem change and thereby alter thespeed rotating gear 68 ofthe pneumatic tachometer of FIGURE in adirection to bring the actual speed reference of input B in balance withthe requested speed reference of input A. This integrated system isshown in FIGURE 15 which will be discussed at a later point.

Surge system The condition known as surging in a gas turbine enginehaving a compressor is related to compressor speed, inlet air velocity,temperature and other variables and parameters. Given enough informationon engine conditions, surging may be predicted by computation, andappropriate preventive action can be undertaken. Surge prediction bycomputation requires several input sensors to gather the required inputinformation, and a computing system to process the information. The factthat the computation cannot be programmed with perfect accuracy requiresthat an appreciable safety margin must be applied such that anti-surgeaction (fuel flow reduction) must be made to take effect safely beforethe actual surge conditions arise. However, when an impending surge issensed directly as against being computed, the complexity of a computerand numerous sensors can be eliminated and a more efiicient avoidance ofsurge is possible. Accordingly, the surge system of the presentinvention utilizes the principle of direct sensing of impending surgeand utilizes all pneumatic components to provide an extremely accuratesurge control with a minimum of structural complexity.

Surge sensing frequently used interchangeably. Refer to FIGURE Avwherein dotted lines indicate normal air flow over the convex or lowpressure surface of a compressor stator blade having an airfoil shapewith an upper convex and a lower concave surface; whereas FIGURE 10Bwavy lines over the blade convex surface indicate air flow during surgeand indicate that the air flow separates from the blade surface. Sincethe separation results in a decrease in lift on the upper trailing edgeof the blade, pressure in this region is increased. A pressure sensor,indicated by passage 212 in FIGURE 10B, is located at the blade convexsurface in the region of separation near the trailing edge and wouldsense the separation as a step of increased pressure. Such a pressuresignal is adapted for use to indicate surging and initiate appropriateanti-surge control functions.

Unfortunately, surging results in reduced engine efficiency andpotential accelerated wear and damage to the engine. For practicalreasons it is undesirable to allow an actual surge condition to develop.A method of predicting surge pre-conditions is required. It has beenfound that separation is imminent in the surge pre-condition state.Therefore, by inducing a transient surge separation on a properlyselected blade the proximity to surge may be sensed without actuallyencountering surge. In the present invention separation is induced whensurge is imminent by applying a short pneumatic pulse through passage214 which is located toward the leading edge of blade 210 in comparisonto pressure sensing passage 212 and in flow alignment along a chordalblade section. By supplying a short pulse through passage 214 a shorttransient separation of air flow will occur if surge is imminent. Thisshort separation will cause an increase of pressure in the trailing edgeregion where it will be sensed by passage 212. When surge is notimminent the initiation pulse supplied by passage 214 will not induceseparation.

Referring to FIGURE 11 there is shown a block diagram of the surgesubsystem and includes a pneumatic pulse generator 216 for supplying aninitiation pulse of known frequency, see FIGURE 6 for fixed frequencyoscillator. Pulses generated in pneumatic pulse generator 216 aretransmitted by passage 214 to a selected compressor stator blade 210.The magnitude of the pulses is made such that separation can be inducedonly when surge is imminent. When a transient separation occursindicating surge preconditions, the increased pressure developeddownstream is sensed by passage 212 and transmitted to a pulse shaper218 (FIGURE 14). Pulse shaper 218, as will be more fully described at alater point, is triggered by the sensed pulses in passage 212 to produceoutput pulses in line 220 of uniform amplitude and duration but of thesame frequency of the sensed pulses in passage 212. Pulses developed inshaper 218 are transmitted to the gate device 222, also to be laterdescribed, to close a gate in the speed-command-pulse path (for examplein path of input A of FIGURE 8) lowering the engine speed and avoidingstall or surge.

Since in the speed control loop, fuel flow is proportional to the pulsefrequency of speed command, fuel flow can be reduced by gating a numberof pulses of input A derived from speed command oscillator (FIGURE 7 Theamount of fuel flow reduction for each surge indication signal isrelated to the number of pulses gated and thus to the time duration ofthe gate pulse. The longer the gate pulse, the more fuel flow and enginespeed is reduced for a given pre-surge separation indication. Thegate-pulse time duration therefore directly influences the. gain of thesurge control function. In addition, since the rate of command pulsesbeing gated is proportional to speed command, the speed reduction persurge gate pulse is essentially a percentage of command engine speed.For a given surge gate pulse duration, the amount of speed reduction fora given surge indication pulse will be greater at high speed commandlevels than at low.

The components of the surge system consist of the pulse generator 216and surge sensor previously described and gate valve 222 and pulseshaper 218 described as follows.

Gate

The basic surge limiting function operates by sensing an impending surgecondition and reducing engine speed to avoid the impending surge.

Since speed command pulses always exist during normal engine running, amethod of reducing engine speed is to reduce the number of speed commandpulses by gating. A closed gate in a pulse transmission line inhibitsthe flow of pulses beyond the gate, essentially reducing the speedcommand signal while the gate is closed. In the surge limiting system ofthe present invention, a pneumatic pulse of specified time duration isgenerated when a surge separation is initiated.

An all pneumatic gate valve of the single input type is shown in FIGURE12. The gate consists of a high pressure supply chamber 224 supplying amain supply stream of pneumatic fluid via passage 226 to supply jet 228.Supply jet 228 ejects the main supply stream into receiving chamber 230which it traverses and flows out aligned vent passage 232 to theatmosphere or the like. An output passage 234 is arranged obliquely withrespect to vent passage 232 and contains an output receiving port 236opening into receiving chamber 230 and spaced offset from the mainsupply stream traversing chamber 230 so that normally the main supplystream does not enter output passage 234, unless, of course, it isdeflected downwardly.

1 l A signal input pulse train is supplied to passage 238 having acontrol jet 246 opening into receiving chamber 230 generally transverseto the main supply stream and ofiset therefrom in a direction oppositeto that of output port 236. So far described, the device acts as asimple pneumatic amplifier. If a signal pulse train is applied topassage 238 the main supply stream is deflected down into outputreceiver port 236 for as long as each signal or control pulse exists.

A gate pulse transmission line 242 is supplied having a control jet 244opening into receiving chamber 230 generally transverse to the mainsupply stream and closely aligned with control jet 240 on the oppositeside of the receiving chamber. When a gate pulse is supplied to line242, its momentum and direction are such that it prevents input pulsesfrom deflecting the main supply stream for as long as the gate pulseexists. The gating or block- 7 ing of one pneumatic pulse by another isthus achieved.

The basic approach illustrated in FIGURE 12 can be used in a gate withmultiple gate signal inputs as shown in FIGURE 13. In this configurationa second gate signal transmission line 246 is added having a control jet248 generally opposed to the signal input control jet 240. Gate pulsessupplied by lines 242 or 246 or both will serve to block an outputsignal in response to a signal input in line 238.

Pulse shaper The shaping or reshaping of pulses is required whenever anexisting pulse form is not proper for an intended use. Thus when eithera generated pulse does not have optimum shape because of thecharacteristic of the pulse generator or when a pulse shape has beendistorted because of attenuation over a length of transmission line, itis desired that the pulse be reshaped to be of uniform amplitude andduration. In the present invention logic is transmitted by means ofpulse frequencywherebyother pulse characteristics such as amplitude andduration are to be held uniform so as not to introduce errors when pulseaveraging is utilized such as for example in the digital to analogconversion of the error computer of FIGURE 8.

In FIGURE 14 there is shown a pulse shaper for utilizing an existingsignal pulse to trigger the generation of a new output pulse ofdetermined amplitude and duration but having the same frequency as thetriggering pulse. The pulse shaper includes a high pressure supplychamber 250, P connect by transmission line 252 to main supply jet 254.The high pressure supply stream ejected from jet 254 traverses receivingchamber 256 and normally flow out vent passage 258 to the atmosphere orthe like. A triggering pulse which is a distorted signal pulse issupplied by passage 260 having a control jet 262 ejecting into receivingchamber 256 generally transverse to the main supply stream. Outputpassage 264 is arranged generally obliquely to vent passage 258 and hasa receiving port 266 opening into receiving chamber 256 slightly offsetfrom the main supply stream in a direction opposite that of control jet262. By design, a small depression or volume 268 is formed in thesidewall of output passage 264 downstream of receiving port 266. Atriggering pulse supplied by passage 260 is ejected by control jet 262and causes an upward deflection of the main supply stream from ventpassage 258 to output passage 264. As the main supply stream flows outoutput passage 264 its rapid velocity aspirates fluid from the volume orregion provided by depression 268 causing a low pressure region whichholds the main supply stream in its deflected condition even after thetriggering pulse has stopped. Thus once deflected, the supply stream dueto passage design has the capability of attaching itself to the wall ofoutput passage 264 somewhat analogous to an electrical push-pull switchhaving a holding coil whereby when once actuated holds in its actuatedstate until a deactivating signal is supplied. It has been found thatthe ability of the main stream to attach itself to a wall in as follows.An acceptable trigger pulse is received in a deflected conditionrequires generally intermediate main stream velocities. If velocity iseither excessive or too low, a sufiicient degree of turbulence does notexist required to aspirate fluid in region 268.

The reset signal for restoring the main supply stream from its deflectedstate back to vent passage 258 is supplied by a feedback circuitcomprised of passage 270.

opening into output passage 264 at a spaced distance downstream ofregion 268. Passage 270 contains a reconnects chamber 274 with feedbackcontrol jet 282.

which ejects into receiving chamber 256 generally transverse to the mainsupply stream.

The pulse generation and shaping operation proceeds passage 260, isejected from control jet 262 and deflects the main stream flow intooutput passage 264. A triggering pulse is acceptable if the magnitude issufiicient or large enough to initiate main stream deflection, thedetailed form of trigger pulse is not important and generally isanticipated to be in a considerably distorted or degenerated condition.Once deflected the main stream attaches itself to the-output passagewall by means of the aspirating effect on region 268. Part of the mainstream flow is diverted through passage 270 into the feedback pathcomprised of restrictions 272 and 280 and the volume of chamber 274. Atime delay in the feedback path is induced by the time required to fillthe volume of chamber 274 and build the pressure in the feedback line toa sufficiently high value whereby when ejected by feedback control jet282 it restores or resets the deflected main stream to its original flowpath out vent 258, thus stopping the flow out output passage 264. Theoutput pulse thus produced, started when the trigger pulse was receivedand lasted until the delayed feedback signal resettthe flow. The outputpulse length is proportional to the feedback delay, whichmay be variedby adjustment of the volume in chamber 274 by means of piston 278.

Referring back to the surge system of FIGURE 11,

as a surge separation signal is generated as stall is approached, thisseparation signal is transmitted to pulse shaper 218 to provide atrigger pulse input. Pulse shaper 218 supplies an amplified output pulsetrain to line 220 wherein the pulses have uniform amplitude andduration, but have the same frequency as the separation signal inputpulse. The pulse shaper pulse output is then fed to gate valve 222 toprovide a blocking gate signal input to reduce the speed command signaland thus reduce engine speed. A fully integrated system showing thespecific interconnections is illustrated in FIGURE 15 and will be laterdescribed.

System i The overall control system schematic is shown in FIG- URE 15and illustrates an integrated pulse control system utilizing thecomponents heretofore described to per- 4 form the functions discussed.

A gas turbine engine generally indicated by numeral 360 consists of anair intake section 362; compressor 364;

flame tube combustors 366 receiving air from compressor 364 and fuelfrom manifold 368 through nozzles 370; a turbine 372 drivingly connectedto compressor 364 by shaft 374; and a tailpipe section 376.

Fuel is supplied to manifold 368 from a fuel sub- As previously statedthe speed control loop is the basic control. Speed command pulse signalis provided by a variable frequency tuning fork oscillator 400 (seeFIGURE 7) having a pulse frequency established by tuning slug 402 whichis adjustable by throttle lever 404. The pulse train in output line 406therefore has a frequency representing speed demand. Depending on thelength of line 406 and the resulting pulse attenuation, one or morepulse shaper 408, corresponding to that shown in FIGURE 14, is arrangedin the line to restore pulse shape and strength while maintaining speedcommand frequency. Line 406 terminates at gate valve 410 (FIGURES 12 and13) which acts as a simple amplifier when no blocking or gating signalsare supplied thus permitting the passage of the speed command signal topassage 138 and provide one control input to error computer 24.

An actual angine speed pulse signal is produced by tachometer 412(FIGURE '5) which is driven in proportion to engine speed by connection414 to provide a pulse train in passage 416 proportional to enginespeed. The actual speed pulse train in passage 416 is fed to pulseshaper 418 to establish uniform pulse shape and is then transmittedthrough passage 420 to gate valve 422. When no blocking signal isapplied to gate valve 422 the actual speed pulse train is amplified andtransmitted to passage 140 as a second input to error computer 24opposing the speed demand signal in passage 138. When actual enginespeed equals that requested by positioning throttle 404 the pulsefrequencies in passages 138 and 140 will be balanced and no error signalis produced thus maintaining fuel delivery at its existing rate. Ifthrottle 404 is adjusted, however, to call for either an increase ordecrease in engine speed, the frequency of the speed command pulse trainwill be changed causing an unbalance in speed demand and actual speedpulse frequencies thus inducing an error. The error operates to positionlever 202 of the fuel subsystem calling for a corrective change in fueldelivery which in turn induces a speed change in the engine. The enginespeed change in turn alters the pulse frequency output of tachometer 412bringing the actual. speed frequency signal back into balance with thedemand signal.

In event speed change is so rapid" so as to approach closely acompressor stall condition, the impending stall sensing system becomesoperative to automatically reduce the speed command signal and avoidstall. The surge system more fully described in connection with FIGURES10 and 11 includes a fixed frequency pneumatic oscillator 424 to supplyan initiation pulse to passage 426 which is applied to the leading edgeof a compressor stator blade 210. More than one stall sensing system maybe used if desired to cover more of the compressor geometry. If stall isimminent, separation of air flow over the blade occurs producing aseparation indicating pulse in passage 428. -The separation pulse is fedto pulse shaper providing a uniform pulse shape output in passage 432corresponding in frequency to that of the oscillator 424 duringseparation. The stall separation signal in passage 432 is in turnsupplied to gate valve 410 as a blocking or gating signal and isoperative to reduce the speed command pulse frequency in passage 138thus calling for a reduction in engine speed which in turn avoids stall.The degree of reduction in engine speed called for is adjusted by.changes in the volume chamber in the pulse shaper 408. A larger volumestretches the pulse thus blocking gate 410 for a longer period of time.When stall is not imminent, no separation signal is produced and speedcommand pulses are not gated by the stall system.

It will be understood that various portions of the invention describedherein may be utilized separately of other components, or may becombined with other and different components without departing from theteachings contained herein.

We claim:

1. A compressor stall sensor comprising: a selected compressorblade-located in a stream of compressor air flow; said blade having agenerally airfoil shape along a chordal section defining a leading edgeextending foremost into said air flow stream, a trailing edge disposedhindmost in said air flow stream, a convex surface extending fromsaidleading to said trailing edge inducing low pressure air stream flowadjacentsaid convex surface, and a concave surface extending from saidleading to said trailing edge and spaced from said convex surface; firstand second openings formed in said convex surface of said compressorblade; said first opening being spaced toward said leading edge along ablade chordal section from said second opening; first passage meansformed in said compressor blade communicating with said first opening;pulse generator means operative to generate a periodic pressure pulse;said pulse generator connected to said first passage to transmitperiodic pulses through said first passage and out said first openinginto said air stream opera-- tive to induce a transitory air streamseparation from said convex surface when stall is imminent to therebyinduce a pressure increase adjacent said convex surface and along achordal length thereof; second passage means formed in said compressorblade communicating with said second opening operative to receive anoutput pressure signal in dicative of impending stall.

2. A compressor stall sensor comprising: a selected compressor bladelocated in a stream of compressor air flow; said blade having agenerally airfoil shape along a chordal section defining a leading edgeextending foremost into said air flow stream, a trailing edge disposedhindmost in said air flow stream, a convex surface extending from saidleading to said trailing edge inducing low pressure air stream flowadjacent said convex surface, and a concave surface extending from saidleading to said trailing edge and spaced from said convex surface; firstand second openings formed in said convex surface of said compressorblade; said first opening being spaced toward said leading edge along ablade chordal section from said second opening; first passage meansformed in said compressor blade communicating with said first opening;

pressure supply means connected to said first passage to supply an airpressure greater than the air pressure in said air stream adjacent saidconvex surface through said first passage and out said first opening toinduce a localized air stream separation from said convex surface whenstall is imminent; second passage means formed in said compressor bladecommunicating with said second opening operative to receive an outputpressure increase indicative of impending stall.

3. A compressor stall sensor comprising: a selected compressor bladelocated in a stream of compressor air flow; said blade having agenerally airfoil shape along a chordal section defining a leading edgeextending foremost into said air flow stream, a trailing edge disposedhindmost in said air flow stream, and a convex surface extending fromsaid leading to said trailing edge inducing loW pressure air stream flowadjacent said convex surface; first and second openings formed in saidconvex surface of said compressor blade; said first opening being spacedtoward said leading edge along a blade chordal section from said secondopening; first passage means formed in said compressor bladecommunicating with said first opening; pressure supply means connectedto said first passage to supply an air pressure greater than the airpressure adjacent said convex surface through said first opening toinduce a localized air stream separation from said convex surface whenstall is imminent; second passage means formed in said compressor bladecommunicating with said second opening operative to receive an outputpressure increase indicative of impending stall.

4. A device for sensing impending stall of an airfoil ina moving airstream comprising: an airfoil member having a generally convex surfacedisposed in a moving air sure supply means connected to said firstpassage to sup- 1 ply an air pressure greater than the air pressureadjacent said convex surface through said first opening to induce alocalized air stream separation from said convex surface when stall isimminent; second passage means communicating with said second openingoperative to receive an output pressure increase indicative of impendingstall on said airfoil.

References Cited by the Examiner UNITED STATES PATENTS Broder et a1.34027 MARK NEWMAN, Primary Examiner.

1o DONLEY J. STOCKING, Examiner. W. L. FREEH, Assistant Examiner.

1. A COMPRESSOR STALL SENSOR COMPRISING: A SELECTED COMPRESSOR BLADELOCATED IN A STREAM OF COMPRESSOR AIR FLOW; SAID BLADE HAVING AGENERALLY AIRFOIL SHAPE ALONG A CHORDAL SECTION DEFINING A LEADING EDGEEXTENDING FOREMOST INTO SAID AIR FLOW STREAM, A TRAILING EDGE DISPOSEDHINDMOST IN SAID AIR FLOW STREAM, A CONVEX SURFACE EXTENDING FROM SAIDLEADING TO SAID TRAILING EDGE INDUCING LOW PRESSURE AIR STREAM FLOWADJACENT SAID CONVEX SURFACE, AND A CONCAVE SURFACE EXTENDING FROM SAIDLEADING TO SAID TRAILING EDGE AND SPACED FROM SAID CONVEX SURFACE; FIRSTAND SECOND OPENINGS FORMED IN SAID CONVEX SURFACE OF SAID COMPRESSORBLADE; SAID FIRST OPENING BEING SPACED TOWARD SAID LEADING EDGE ALONG ABLADE CHORDAL SECTION FROM SAID SECOND OPENING; FIRST PASSAGE MEANSFORMED IN SAID COMPRESSOR BLADE COMMUNICATING WITH SAID FIRST OPENING;PULSE GENERATOR MEANS OPERATIVE TO GENERATE A PERIODIC PRESSURE PULSE;SAID PULSE GENERATOR CONNECTED TO SAID FIRST PASSAGE TO TRANSMITPERIODIC PULSES THROUGH SAID FIRST PASSAGE AND OUT SAID FIRST OPENINGINTO SAID AIR STREAM OPERATIVE TO INDUCE A TRANSITORY AIR STREAMSEPARATION FROM SAID CONVEX SURFACE WHEN STALL IS IMMINENT TO THEREBYINDUCE A PRESSURE INCREASE ADJACENT SAID CONVEX SURFACE AND ALONG ACHORDAL LENGTH THEREOF; SECOND PASSAGE MEANS FORMED IN SAID COMPRESSORBLADE COMMUNICATING WITH SAID SECOND OPENING OPERATIVE TO RECEIVE ANOUTPUT PRESSURE SIGNAL INDICATIVE OF IMPENDING STALL.